Friction stir welding (FSW) is a process for joining metals without fusion or filler materials. FSW is used routinely for joining components made of aluminum and its various alloys. Indeed, it has been convincingly demonstrated that the process results in strong and ductile joints, sometimes in systems which have proved difficult using conventional welding techniques. The process is most suitable for components which are flat and long (plates and sheets) but can be adapted for pipes, hollow sections and positional welding. The welds are created by the combined action of frictional heating and mechanical deformation due to a rotating tool. However, joining dissimilar materials with significantly different properties (e.g., melting temperatures and densities) is problematic for most welding methods, because the lower temperature melting material can liquefy and be removed from the desired bonding area before the higher melting temperature material melts and before the weld can form. In general, conventional FSW between dissimilar materials yields unstable lap weld joints due to the vastly different melt temperatures and flow stress properties of the materials. Wide statistical deviation in the resulting lap welds is a common result.
The present invention disclosed herein provides for lap welding between dissimilar materials. Additional advantages and novel features of the present invention will be set forth as follows and will be readily apparent from the descriptions and demonstrations set forth herein. Accordingly, the following descriptions of the present invention should be seen as illustrative of the invention and not as limiting in any way.